It is known that automotive glass is mounted with inner mirror-mounting brackets, camera sensor-mounting brackets, molding, protectors, positioning reference pins, door glass-fastening holders, hinges, and like members. Various adhesives, such as epoxy-based adhesives, urethane-based adhesives, silicone-based adhesives, and modified silicone-based adhesives, are conventionally used to mount these members. Epoxy-based adhesives, urethane-based adhesives, silicone-based adhesives, modified silicone-based adhesives, and like adhesives are generally used.
In particular, polyurethane adhesives comprising polyurethane as a main component and containing a plasticizer, a filler, a pigment, etc., are widely used as joint materials, sealing materials, adhesives, covering materials, and the like, as well as for direct grading for bonding an automobile glass and an automobile body. Polyurethane adhesives used for such purposes are moisture-curable adhesives and classified into one-component type and two-component type adhesives, both of which are cured by a crosslinking reaction promoted by the moisture in the air.
Moisture-curable adhesives are very slowly cured under low-temperature conditions in winter, and the completion of the crosslinking requires several days. In particular, one-component type polyurethane adhesives significantly show this tendency. As a method for increasing the effect of such a moisture-curable adhesive, a method of placing the adhesive in a high-temperature aging room is known; however, even curing in an environment at 30 to 40° C. and 55 to 60% RH requires 8 hours or more. It is difficult to significantly improve the efficiency.
Moreover, a relatively large space was necessary for storing the automotive glass for 8 hours or more. Therefore, it was necessary to provide a large storage space apart from the production line, which problematically increased the number of transportation steps in the production of automotive glass. Furthermore, adhesive-curing required facilities, such as an aging room for controlling humidity etc. Thus, large-scale capital investment was necessary.
In recent years, as a technique that enables production in a highly efficient and space-saving manner, without the need for an aging and drying process after bonding, a technique for promoting curing of thermosetting adhesives by high-frequency induction heating has been developed (PTL 1 etc.).
There are various shapes of automotive glass depending on the design and size of vehicles, and accordingly there are various sizes and shapes of parts. Therefore, a process using high-frequency induction heating requires the preparation of plural high-frequency induction heating devices for every type of car according to the size and shape of the part. Moreover, the curvature of a portion to which an adherend is to be attached varies depending on the type of glass. When high-frequency induction heating is performed on glasses different in their curvature, the distance (clearance) between two sides varies in many cases. The thermosetting adhesive is not completely cured, or the temperature overly increases such that the glass scorches. Thus, there was a problem such that stable quality could not sufficiently be obtained in the production of automotive glass to which a part was attached. Furthermore, when the adherend was plastic, the heat resistance of the adherend was low, and the adherend itself was synchronized with high frequency, causing heat generation. As a result, the adherend melted. Thus, there were various problems. Hence, there has been a demand for processes that overcome these problems.